Mauro Icardi celebrates Inter’s victory at the end of their match with Juventus.
Photograph: Pier Marco Tacca/Getty Images

There was no witty pun on the front page of Friday’s Gazzetta dello Sport, no attempt to make mirth out of Inter’s Europa League defeat at home to Hapoel Be’er Sheva. Instead, only a damning question: “Inter, aren’t you ashamed?”

A national newspaper, but also a Milanese one, Gazzetta can sometimes be more generous to the city’s two leading clubs than they really deserve. Not this time. The tone of the coverage was such that you almost expected to find an editorial inside calling for the Nerazzurri’s starting XI to be stripped naked and harangued by a woman with a bell on a walk of atonement from San Siro to The Duomo.

Such righteous anger had its roots in more than a single bad result – even if this might have been the most embarrassing one that the club had endured since the 1987 defeat to Turun Pallouseura. Gazzetta’s journalists had simply lost patience, like many supporters, with a team that has failed for half a decade to play up to its potential.

Following José Mourinho’s departure in 2010, Inter slipped to second, sixth and then ninth in the standings over successive seasons. In the last two summers, they have spent more than €200m on new signings in an attempt to right the ship. There have been sales, too, but only to a value of about half of that sum.

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And yet progress has remained painfully slow. Sure, Inter rose from eighth to fourth last season, but they were still 13 points behind third-placed Roma. And if the club’s new Chinese owners from the Suning Commerce Group are aiming for a return to the Champions League at the first possible opportunity, then it can hardly help their long-term branding goals to be embarrassed in a lesser competition in the meantime.

Among the countless ways that you could illustrate Inter’s decline is with their results in the Derby d’Italia. Since winning the treble in 2010, the Nerazzurri had beaten Juventus in the league just once, and never in front of their own fans. The knowledge that this fixture was coming up on Sunday only cast Thursday’s result into even sharper focus.

There had been few enough reasons even beforehand to believe that Inter could spring an upset. They had won one of their first three Serie A games this season, and even then required an injury-time goal to squeeze past newly-promoted Pescara.

Up until the Hapoel defeat, most commentators were prepared to forgive such a slow start. Inter’s new manager, Frank de Boer, had only taken up his post on 9 August after relations between Roberto Mancini and the club’s new owners soured. The squad that the Dutchman inherited was in poor physical condition, with fitness regimes neglected amid a busy summer schedule of exhibition games abroad.

De Boer himself said it would take four months to put his mark on the side. His bolder decisions were still questioned by the press – and in particular the experiment with an untested three-man defence during an opening defeat to Chievo – but overall patience prevailed. Now, though, the situation felt more urgent. If Inter could not even avoid humiliation against the champions of Israel, then what would happen when the team that had won Serie A for five seasons running paid a visit.

The answer to that question was not what most people had expected. Juventus, coming off an underwhelming draw of their own in midweek against Sevilla, still looked disjointed. The shape of their 3-5-2 was all wrong, with Miralem Pjanic struggling to interpret an unfamiliar role as a deep-lying playmaker. Gonzalo Higuaín had been left on the bench, and his replacement up front, Mario Mandzukic, was anonymous.

By contrast, Inter, encouraged by a crowd of more than 76,000, played with a fire and aggression embodied by the marauding Mauro Icardi. In the 38th minute, he withstood a shoulder-to-shoulder charge from Giorgio Chiellini inside the penalty box, leaving the defender flat on his back before twisting back to fire in a vicious shot that grazed the far post.

Juventus had their own chances, inevitably, and would already have been ahead if Sami Khedira had shown any conviction with his header when unmarked and bearing down on goal. But on balance, Inter were shading it – as well as dominating physically with their aggressive high press. Icardi, who teed up Antonio Candreva for another near-miss, looked easily the most dangerous player on the pitch.

And then, inevitably, Juventus scored. Alex Sandro made it look so easy as he breezed past Danilo D’Ambrosio on the left, before crossing for Stephan Lichtsteiner to slot home. As scripts go, this one felt all-too familiar. Inter, even on a good day, were still Inter. Champions know how to close.

Only, Juventus must have forgotten. Because within two minutes, Inter were back level – Icardi timing his run perfectly to meet Éver Banega’s corner with a thumping header past Gianluigi Buffon. A goal was the least that he deserved for a performance that had mixed finesse and fury in equal measure. But Icardi has never really been a man to settle for “leasts” or indeed whatever it is that other people think he deserves. He showed as much this summer, negotiating hard for a new contract (or at least allowing his wife and agent, Wanda, to do so) despite criticism from fans who remember him receiving a pay rise just last year.

He showed as much again on Sunday, delighting those same supporters by refusing to content himself with a draw. In the 78th minute, Icardi ran on to a chipped pass from Candreva down the right channel, drawing both Buffon and Leonardo Bonucci in pursuit. As they collided down by the goal-line, Icardi span and delivered a gorgeous outside-of-the-boot cross to the head of Ivan Perisic. The Croat nodded it home.

San Siro erupted. Juventus had finally sent on Higuaín to partner Paulo Dybala a few moments earlier, but this day belonged to the Argentinian in the blue-and-black stripes. Inter held on to win 2-1, and nobody could doubt that Icardi – even if ably assisted by Candreva and especially João Mário – was the star of the show.

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On a day like this, that improved contract, worth a reported €4.5m per season plus bonuses, starts to look like a snip. If it is true that Icardi has long tended to reserve his best performances for Juventus – he has now scored against them seven times in eight games – then what he showed here was that he is growing into a far more rounded player than he was once thought to be.

Inter would do well not to get carried away. There were flaws on display here as well, and they have conceded first in every game that they have played under De Boer. But there could be no better tonic than this for Thursday’s humiliation. Monday’s Gazzetta front cover called Inter “Crazy” – hardly an insult, given that they sing about such traits in their own official club anthem. Still, this time La Repubblica might have said it even better, with a simple, “Welcome back”.

Talking points

• Joe Hart’s second game in Italy turned out to be rather more serene than his first. He didn’t have a whole heap to do against Empoli, but responded well when called upon – taking the ball off the toes of Manuel Pucciarelli following a bad leave from Leandro Castán – and secured his first Serie A clean sheet. Most of all, I, like many in Turin, was impressed with the commitment he is showing to learning Italian and integrating properly into his new setting. And having had the good fortune to speak to a couple this weekend, I can confirm his team-mates feel the same way.

• Taking advantage of Juve’s dropped points to go top were Napoli, who beat Bologna 3-1 and have now scored 12 times in their opening four games – making this their most prolific start to a Serie A season since 1957-58. For the first time this season they even scored a goal without Arkadiusz Milik on the pitch, though he was still the man who came off the bench to grab a brace and seal the points.

• Sassuolo continue to astonish with the start they have made to this season. The Neroverdi could have been forgiven some tired legs after thrashing Athletic Bilbao 3-0 on Thursday night but instead they continued to look like a team with the bit between its teeth as they saw off previously undefeated Genoa as well. More impressive still, both victories were achieved without the injured Domenico Berardi.

• Roma’s run of 20 games without a loss in Serie A came to an end with a 1-0 defeat away to Fiorentina. If the Giallorossi could count themselves unfortunate with a few key refereeing decisions – for the winning goal itself, Nikola Kalinic had been stood in an offside position and obstructing Wojciech Szczesny’s view of the ball – theirs had also been another disappointing performance at a time when they ought to have been pressing hard to capitalise on Juve’s slip. It is hard to shake the sense that the failure to qualify for the Champions League groups has had a detrimental knock-on impact in the league – much as it seemed to do for Napoli two years ago.

• The most moving images of the footballing weekend came from Cagliari, where Fabio Pisacane wept after making his Serie A debut at 30 years old. Half a lifetime ago, at 14, he was diagnosed with Guillain-Barré syndrome – a condition which caused him to experience temporary paralysis in his limbs and for a time to fall into a coma. He recovered fully and has gone on to enjoy a solid career in the lower leagues, even getting called up to train with the Italian national team in 2012 as a reward for his bravery in reporting a director of a rival club who had tried to persuade him to fix a match. But to play in the top flight was his real dream, and one which he thought he had lost as a teen.